It Was A Mistake
by spaceman-earthgirl
Summary: Beckett leaves Castle a note after their first night together but he doesn't see it. He wakes up alone and thinks she's left after regretting what they'd done. Always AU.
1. Chapter 1

This accidentally happened when I was working on my other fics. Two-shot, the second chapter will be up in a few days.

Always AU-Only differences are that Beckett didn't quit, Esposito wasn't suspended and Martha and Alexis don't show up in the morning.

**Disclaimer: I don't own Castle or the characters.**

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Richard Castle hadn't woken up feeling this great in a very long time. He didn't want to open his eyes as visions of Beckett from the previous night flashed through his mind. He stretched out, eyes still closed, reaching for her. When he felt nothing but cold he rolled over, his arm knocking the pillow from the other side of the bed onto the floor, knocking the note Beckett had left him with it.

He looked around and there was no sight of her in the room or any evidence that she'd ever been there.

"Beckett?" he called out but there was no response. He dropped his head back onto the pillow, his good mood vanishing. Where was she? Had she snuck out after he'd fallen asleep or waited until the morning? Had she just left for work but hadn't wanted to wake him or did she regret what had happened between them?

He lay in bed for a while after that, just thinking. He considered texting her but decided against, wanting to have the conversation he assumed was coming in person. If she was just simply at work and had left him sleeping then he would've just texted her but he wasn't sure that was the case. If she did regret what had happened last night, if she didn't want him, she'd have to tell him to his face, she wasn't getting away with it that easily. And he was going to fight for her too, try to convince her that what had happened wasn't a mistake and that they could be great together.

He loved her and he was going to prove it to her. With that thought in mind he finally got out of bed having decided to go into the precinct to find out exactly what was going through her mind.

Castle felt better when he finally did show up at the precinct later that day, anxious to see her, but his confidence left him as soon as he laid eyes on her. What was he meant to say? Just go up to her and say "I love you" in the middle of the crowded precinct? He could ask to speak to her somewhere more privately, but what if she said no? Or said yes but then told him she wanted to forget last night had happened and return to being friends? Castle didn't think his heart could take that right now and if he said nothing, he could at least for now pretend that there may be more of a future for them than just being partners at work.

XXX

Beckett had been waiting for Castle all morning, wondering what was taking him so long to arrive at the precinct. Should she text him? He would've texted her if he hadn't been coming in, right? She was just about to text him when she looked up and saw him in front of her.

And immediately she could tell something was wrong. She expected to see him happy and smiling with coffee in his hand when he arrived and while there was coffee, he certainly wasn't smiling. The look he was giving her was not the one she wanted to see, the one where he looked at her with such love and happiness that she had no doubt about how he felt about her. She thought maybe she did see that same love in his eyes now but it was hidden behind something she couldn't quite decipher and there wasn't a trace of happiness.

Hi," Beckett said, with a smile that didn't quite reach her eyes as she tried to figure out exactly what was on Castle's mind.

"Hi," he replied, handing over her coffee before taking his own seat at her desk.

This wasn't anything like what Beckett had expected when he arrived this morning. She expected jokes, and happiness and flirting and Castle trying to get her alone so he could at least kiss her. But none of that was happening though, he just sat their quietly playing on his phone while she did paperwork.

Beckett was about to say something, ask if they could speak alone because it had been over an hour since he arrived and he had said hardly a word and she couldn't stand not knowing what was wrong with him. Had she done something wrong, something that upset him or did he just simply regret what had happened last night and wanted to pretend like it had never happened?

But then her phone rang and she lost her chance. She ended the call after noting down the crime scene address but now there'd be no time for talking because they had a body, although there was the car ride to the scene which would be a perfect chance to talk to-

"I'm going to ride with Ryan and Esposito," Castle said, cutting off her thoughts and making her chest tighten because it was looking more and more like he regretted last night and she didn't know how to handle that.

"Ok," Beckett replied, before quickly giving the boys the address and saying she'd meet them there because she couldn't bear to look at him anymore and see the unknown emotion in his eyes.

XXX

He didn't like her leaving like that, didn't like the hurt look in her eyes when he told her he was going to get a ride with the boys to the crime scene but he just didn't think he could handle being alone with her right now. Just looking at her brought back memories of last night which was quickly followed by wanting to touch her again as well as the thought that he may never be able to again, they may never get a chance to be together and so he decided that being apart from her for at least for a little while would give his heart a break.

XXX

The crime scene was okay because they had distractions, Lanie giving them details and talking to the witnesses but now back at the precinct there was nothing to stop them talking. But this was a conversation that Castle didn't want to happen here where there wasn't much privacy and he didn't really even know what he was going to say so he stuck close to Ryan and Esposito to avoid having to be alone with Beckett.

Beckett tried several times to speak to Castle but he kept deflecting, saying he was busy and that they could talk later.

Beckett was getting frustrated now and just wanted to know what was wrong with Castle. And she was also getting worried, surely he didn't regret what they'd done, the step in their relationship they'd taken. He was acting strange and Beckett wanted to know why.

She was relieved when they got to the stage where no more work that could be done today as they were waiting on the lab so Gates told them all to go home early. Castle almost invited Beckett over to the loft to talk but he needed more time. More time to formulate a plan, figure out exactly what he was going to say, which arguments he could use to show Beckett they should be together, that they'd be great together. This morning he'd been so confident about what he was going to do but now he realised he didn't know exactly what to say and he at least wanted some time away from her to find the perfect words to make her see what he does.

"Castle, can we-"

Castle cut her off, "can we do this later, after the case?"

"I-" she didn't get to finish her sentence again.

"I'll see you tomorrow," Castle quickly replied before turning and heading towards the elevator. And if he hadn't have been so preoccupied trying to figure out what he was going to say in their future conversation, he would've seen the hurt look in her eyes and knew he was making a mistake leaving her like this.

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Thoughts?


	2. Chapter 2

So I said this was meant to only have two chapters but I also said the next chapter would be up in a few days and it's been a few days and it's not quite finished so I've split this chapter in two. The final chapter will be posted sometime next week.

Enjoy!

**Disclaimer: I don't own Castle or the characters.**

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Beckett didn't know what to do. Castle had just left her at the precinct and she wasn't sure what was wrong with him. He'd avoided her attempts to get him to talk all day long even though she'd tried several times which was very unlike him.

She could go after him but she didn't know what to say and she didn't want him to shut her down again. But also having to wait until tomorrow to talk to him didn't sound like a good idea either. She was desperate to know what was wrong with him and what she could do to help fix it.

She sat there thinking for a few minutes, trying to decide what she should do when she had an idea: Lanie. She'd know what she should do or at least it would help to talk to someone.

With that thought in mind she quickly dialed her friend's number.

Beckett wasted no time once Lanie had answered the phone to get straight to business.

"Hey, it's me, you nearly finished work?"

"I was just about to leave, why, what's up?"

"Are you free tonight? I need some advice about something." She really hoped Lanie was free, she was the only one she could really talk about Castle to, besides the man himself of course.

"Let me guess, Castle's involved somehow?" Of course Lanie would know it was something Castle related, but honestly, it usually always is.

When Beckett didn't reply straight away, Lanie continued, "Meet at my place in half an hour?"

Beckett let out a breath she didn't realise she was holding, "Yeah, thanks Lane, I'll see you then."

XXX

Beckett turned up at Lanie's half an hour later and she knocked on the door with more confidence than she'd felt all day.

Lanie invited her in, offered her a glass of wine, which Beckett declined because she wanted to be clear headed tonight, and then waited until they were both sitting to talk.

Before they began talking about Beckett's problem with Castle, Lanie had to make sure her friend was okay after what had happened yesterday. They'd talked about it earlier but she wanted to check again. Once Beckett had assured her she was okay with that and that was not what she was here to talk about, Lanie let it drop and instead asked about what her problem with Castle was.

"So, what's up?"

"I don't know," replied Beckett, knowing that wasn't what Lanie was exactly asking but it was the truth.

Lanie stayed silent, waiting for Beckett to elaborate.

"it's just...," she paused, "Castle's just..." she paused again, not knowing exactly how to put into words what she was thinking,"today, he's been different, and I don't know why, or what I did to make him act that way. Well maybe I do but it still doesn't make sense."

"Woah, slow down," replied Lanie, not following what Beckett was talking about, "and start from the beginning."

Beckett took a deep breath before she began, "After everything that happened yesterday I realised something, something that I had to tell Castle," Beckett paused then, not sure how to tell her friend what happened next. Lanie waited patiently for Beckett to continue so Beckett decided to tell her everything, that was the only way she'd be able to get proper advice from her friend.

"Castle and I had an argument and he basically told me our partnership was over. I then went over later to apologise and to tell Castle what I'd realised, that I wanted him," Beckett paused again, but this time because she knew Lanie wanted the rest of the story and she was going to have fun telling her.

"And?" Lanie asked, once she realised Beckett was just stalling to tease her.

"And we ended up making out against his door," Beckett said quickly, wanting to see Lanie's reaction.

"What!"

"And then we had sex."

"What!"

"Several times."

"What!" replied Lanie again, resisting the urge to hug Kate or jump up and down with excitement, "I don't see the problem?"

"Neither did I until he turned up at the precinct and he seemed mad at me, or upset, or something. I don't know what it was, but he wouldn't talk to me all day no matter how much I tried and I tried again before he left but he just asked if we could talk later and before I could reply he was gone," said Beckett, glad she could talk to someone else about this.

"You think he regrets it?"

"I don't know." She really didn't but what else could it be?

"Surely not, that boy has been in love with you for years."

"What else could it be?" Beckett had been asking herself that question all day and the only other thing she'd come up with was that he was mad that she'd left early this morning without waking him but she'd left a note and Castle knew she had to be at work so it didn't make sense that he was that mad, mad enough to not talk to her.

"You said you knew he was different when he arrived at the precinct, what about before that, when you woke up together?"

"We didn't wake up together, I didn't want to wake him so I left him a note and went to work." It made sense at the time to just leave a note but now she wished that she'd at least woken him to say goodbye, at least she would've known then and there if he'd regretted it. Now she'd been left wondering all day what was wrong with him.

"Could he be upset about that? What did the note say? He doesn't think you ran, does he?" Lanie had to make sure herself that Beckett wasn't running but if the rest of this conversation was anything to go by then she didn't think that that was the case.

"I don't think so, the note was pretty basic, just saying I didn't want to wake him and I'd see him at work but I even put a little "x" at the end so there was no other way he could've taken that."

"Kate Beckett, look at you, putting little "x's" on your notes to Castle," Lanie said, a teasing lilt in her voice, she paused then before she continued, "you really love him, don't you?

"I do, I love him so much," replied Beckett and her tone of voice told Lanie she really did mean it.

Beckett realised that was the first time she'd actually said it out loud so she continued, "and that's why I have find out what's wrong, what I've done and how I can fix this because I can't lose him now."

"Do you have a plan?"

"Talk to him? If he'll let me. I just don't know if I should wait or not, I don't want him to push me away any more," and that's what Beckett was afraid of, if whatever was wrong was enough for him to push her away completely and they'd never get a chance at exploring this thing between them. That would truly break her heart.

"I say go now, turn up at his loft and don't take no for an answer. Ask him what's wrong, tell him how you feel and tell him that you want to be with him because I don't believe for a second that that man regrets sleeping with you and whatever this is it's probably just some misunderstanding. He loves you Kate, and you love him, and once he knows that I'm sure you can figure everything else out. Because I know you two belong together, everyone else knows it and now it's time for you two to know it too."

Beckett couldn't help the smile that spread across her face at her friend's words. Lanie was right, they loved each other and she had to go talk to him right now, to try and fix whatever was wrong because right now Castle was unhappy and she wanted to change that as soon as she could.

"Thanks, Lanie," said Beckett, standing up to give her friend a hug, "you're the best."

"Any time, let me know how it goes?"

"Of course, I'll call you later." With that Beckett turned and left, heading to Castle's loft. She was ready now, ready to tell Castle how she felt, to confront him and find out what's really wrong.

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Thoughts?


	3. Chapter 3

So here's the last chapter. Thanks to everyone who has reviewed/favourited/followed this fic, I didn't expect the response it got so thanks.

Enjoy!

**Disclaimer: I don't own Castle or the characters.**

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Castle wanted to see her, he desperately did, but he had no idea what he'd say when he did. He hated this, not talking to her, and while he knew it was his choice, he had to get this right, had to make her see what there was between them and how great they'd be together.

He'd been home for about an hour now and he'd spent the entire time pacing his office trying to figure out exactly what to do. Go talk to her. That was all he'd come up with so far and while that was a good plan, he had no idea what he'd actually say. He's usually so good with words, what is it about Kate that makes it so hard to choose the right ones? But he already knew the answer to that, she was it, she was the women he wanted to spend the rest of his life with. People search for years trying to find the "one" and he'd found his so he couldn't let her slip away now.

He made his way into his bedroom, thinking maybe a change of view would help him think better. It didn't help at all. In fact, it made it worse. While he was still thinking about Beckett, he was now thinking more along the lines of what exactly they'd done last night and what he'd like to do to her the next time he saw her and less about what he'd actually say to her.

He was going to venture into the living room where there'd be less distractions, when he thought he should at least make the bed since it was a reminder of exactly what happened in it last night. He figured that making it now would be less painful than making it later before having to sleep in it. Although he'd probably sleep in the guest room, sleeping in his own bed after what he and Beckett had done in it last night would mostly likely prove to be very distracting.

Castle pulled up the covers, tucked them in and then straightened them up. He noticed a pillow on the floor that must've been knocked off sometime during the night and he was about to bend down to retrieve it when the door bell rang. Abandoning the bed making, he made his way to the door, fleetingly hoping it would be Beckett but knowing it wouldn't be.

"Beckett?" Castle said when he did open the door and saw her standing there. What on earth was she doing here?

"Hi," Beckett replied, standing in Castle's doorway and feeling very nervous about the conversation they were about to have.

"Can I come in?" Beckett continued when Castle just stood there staring at her, a look of disbelief on his face. Was he really so surprised that she'd come to see him?

Castle paused, knowing he probably couldn't put this off conversation any longer, he finally answered, "Of course." He'd have liked a bit more time to think through his argument of why they should give this thing between them a shot but her being here must be a good sign, right? Unless she came to tell him they're over but he tried not to think about that part.

Beckett declined Castle's offer of food or drink once she was inside and she was relieved that he seemed to be past avoiding her, although that would be a lot harder to do when they're alone at his loft but the fact he invited her in was a good start.

They both sat in silence then, neither knowing how to start this conversation without knowing how the other felt. Right now there was still hope, but if the conversation went bad, this could be the end of their relationship for good. Of course neither of them wanted that but working with someone you have strong feelings that are unrequited would be too difficult for both of them.

Beckett was the first to break the silence, she had been the one who had come here to talk after all.

"Can we talk? I really need to tell you something and I know you were avoiding me all day but please Castle, just hear me out?" She really needed him to listen to what she had to say. And it was now or never, she didn't want to wait any longer to find out what was going on with him.

"I'm sorry about avoiding you, I just needed some time to think," replied Castle. He'd felt bad all day avoiding her but he hadn't known what else to do.

_What did he need to think about?_ thought Beckett, _that doesn't sound good._

"But we can talk, I think we need to," continued Castle when Beckett hadn't spoken.

"Okay." She paused, "but first I just need to know one thing before I continue, and I want you to tell the truth, no matter what it is."

She waited for Castle to agree and when he replied with "okay," she continued, "Last night meant something to you, right? It wasn't something you did just to get it out of your system?"

Castle's mouth actually fell open in shock, did she honestly not know how he felt about her?

"Kate, how could you even think that? Of course that's not what it was, I-"

Beckett cut him off, "I didn't know what to think when you spent the entire day avoiding me."

"What was I meant to do? What was I meant to think when I wake up and you're gone," answered Castle, getting slightly worked up, the rollercoaster of emotions from the day finally catching up with him.

"I didn't want to wake you, I thought you might appreciate the sleep in after the last few days," replied Beckett, what was wrong with him, hadn't he seen her note?

"And how was I supposed to know that you weren't running, that you didn't regret last night?"

"Castle-" he cut her off this time, he was on a roll now and didn't want to stop.

"You're constantly pushing me away. Every time we get close you push me away again and I've been patient, I have, but something finally happens between us and then I wake alone and all I can think is that you've run again, or that you realised this isn't what you want, that you regret last night, and that hurts Kate, it hurts so much. So I avoided you today, wanting time to formulate a plan, wanting time to figure out how to show you how much you really mean to me and how great we'd be together."

"Castle-" again, he cut her off.

"And then the first thing you do afterwards is ask if I just slept with you to get it out of my system, like being with you means nothing to me when it means everything." He'd just shown his hand but that didn't matter, she had to know how he felt about her.

He was breathing heavily and his heart was pounding but now the ball was in her court, he'd made his feelings known and now it was up to her.

"Oh Castle," Beckett said, moving closer to him and placing her hand on his cheek, not realising what she'd done to him, how much she'd hurt him.

He lent into her hand, savouring the warmth that was emanating from it, from her, and wanting to be even closer.

"Did you not see it?" she asked, her thumb caressing his cheek as his eyes fell closed.

"See what?" he murmured, now with some hope that his feelings were at least, in part, reciprocated.

"Hold on," she replied, and then the weight of her palm against his cheek vanished and he opened her eyes to see her walking away towards his room to which she vanished into.

He sat for a moment, about to get up and follow her but then he saw her returning, a piece of paper now in her hands.

She stopped just in front of him, and held the paper out for him to take. _What was this?_

He took the paper from her outstretched hand and then as she sat down next to him, he looked down at the white slip of paper now in his hands.

Castle's breath caught when he saw the words written on the page in familiar handwriting.

**Didn't want to wake you, see you at the precinct. x**

His eyes widened as he realised the true meaning of the words, that she hadn't run at all.

"It was under the pillow on the floor, you must've knocked it off the bed and not realised it," said Beckett as Castle just sat starring at the note in his hands.

Beckett's words seemed to snap him out of whatever he was thinking because he turned then to look at her and the next thing Beckett knew he was pulling her close and his lips were on hers.

"I'm so sorry," Castle said after he'd pulled away, but not too far, his forehead was now resting on hers.

"I'm sorry too, I should've at least woken you to say goodbye," replied Beckett, enjoying their closeness and so relieved that their relationship wasn't ruined by what happened yesterday.

Castle pulled back further then, cupping Beckett's face between his hands, "You have to know this Kate, I am in love you," he paused to kiss her, "I am so completely in love with you."

"I know Castle," she replied with a smile, kissing him again, "I know."

"And you're it for me, you know that, right? I'm in this, you and me, forever." They'd technically been going out for a day, and half of that was spent not speaking, but she had to know, he didn't want her to doubt them at all.

"Me too," she smiled, resting her forehead back against his. She wasn't quite ready to say the "I love you" words back to him yet but she knew she felt them and was sure Castle knew now too.

Castle looked back down again at the note she'd left him and smiled.

"That little "x" you put at the end of this is cute," he said, gesturing to the note that was in his hands again.

"It's not cute," she replied, pouting slightly but glad that they are back to this now, the teasing.

"You're right, it's not cute, it's adorable," he answered, grinning as she pouts even more.

"You're adorable," she said, not being able to stop the smile that spread across her face at seeing him grinning like that.

It was his turn to pout, "I'm not adorable."

"Yes you are," she answered, kissing the pout from his lips.

"I'm sorry for today, it was a mistake not waking you," said Beckett, pulling her head back so she could look him in the eyes.

"And it was a mistake not just talking to you about it earlier," replied Castle, if he had have just spoken to her sooner, maybe this whole day of confusion and hurt could have been avoided.

"How about we just call it even?" suggested Beckett, smiling when she say the smile spread across Castle's face.

"Deal," he replied, pulling her forward to kiss her again, something that was quickly becoming one of his favourite things to do.

So maybe they'd both made some mistakes this past day and in the few years that they've known each other. But things were good now, they were finally on the same page, where they could both imagine a future together.

And the next time they did sleep together, that very night, it definitely was not a mistake.

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Thoughts?


End file.
